A major goal of this research is to continue with the characterization of the protein of isolated and purified photoreceptor complexes and reaction center complexes prepared from photosynthetic bacteria, particularly those from R. rubrum. We plan to complete the amino acid sequence determination of one of the major polypeptides (a light-harvesting protein) which we have isolated in large quantities in pure form from R. rubrum. Since a light-harvesting protein is also easily isolated from each photosynthetic bacteria so far studied, much might be learned by comparing the amino acid sequence of several of these. Once the amino acid sequence of this integral membrane protein is known, its three dimensional relationship to the membrane will be systematically probed. Further characterization of the photoreceptor complex from R. rubrum will continue. The next goals are to (a) confirm the functional role of the LH protein; (b) probe the structural requirements and molecular mechanism of the primary photochemical event by exchanging bacteriochlorophyll analogues for the primary electron donor unit and quinone analogues for the first stable electron acceptor; (c) separate the reaction center from the antenna complex and isolate the polypeptides of the reaction center in sufficient quantities for characterization and eventual sequence determination work; (d) reconstitution of activity experiments will be conducted at a fundamental level involving generation of a photoreceptor complex from the purified components (pigments, polypeptides, ubiquinone, etc.).